Careful frequency planning is required for building up a cellular network based on frequency division multiple access (FDMA or TDMA/FDMA principle). The basic idea in cellular networks is to reuse the same frequencies over and over again in order to make a limited band of frequencies to serve a large number of users. Normally the frequency reuse is implemented so as to obtain the highest possible capacity from a frequency band available. A cellular network is typically planned as a monolithic unity, and therefore, any change in the transceivers of the network (installation of a new transceiver, change of operating frequency) requires a checking of the frequency planning of the entire network.
Except by frequency planning, the radio system of a cellular network is made monolithic by network configuration information. Neighbouring cells are assigned for each cell, and a list of neighboring cells is transmitted continuously on a broadcasting channel of the cell to the mobile stations. Based on this system information, mobile stations in idle state monitor the field strength of the current cell and the neighboring cells and select a new cell if the field strength of the current cell becomes too weak. In the same way, mobile stations having an ongoing call via a base station of a serving cell are capable of monitoring the field strength of the assigned neighboring cells. On the basis of the obtained field strength information it is possible to make handover decisions in the cellular radio network. The neighboring cells are defined by means of their frequencies. The transmission of the network configuration information on the broadcasting channel of the cell is an essential precondition of an operation of a conventional cellular radio system, making it possible to maintain an uninterrupted connection between the fixed network and the roaming mobile stations.
Planning a radio network is a laborious measure. Due to the costs, the risks caused for the network operation as a whole, the seriousness of changes to be made in an operating network and the rather long time needed for the whole operation, an existing radio network configuration will not be modified without strong arguments. The operation of the network and business activities utilizing the network must be adapted to the reality that an implementation of a radio network cannot be changed without heavy investments. This reduces the possibilities of the operator of reacting quickly to the varying needs of the customers or to the needs of new customers. Such a capability of reacting would be required, often locally, e.g. for implementation of radio solutions complementing the basic services of the network.